The present invention relates generally to multi-well sample plates, commonly referred to as microtitre plates or microplates, or strips which can be assembled into a carrier frame to produce an analogous component. These microplates are commonly used to hold a large number of samples in a rectangular array of wells, (24 wells (4.times.6) or 96 wells (8.times.12) being typical examples), to be assayed using various techniques such as scintillation counting, luminometry, fluorimetry, and kinetics. This invention is particularly, though not exclusively, concerned with applications which utilise microplates in assay techniques which are dependant on the emission of light from the sample, as would occur in scintillation counting, fluorimetry or luminometry, or on the transmission of light through the sample, as would occur in optical densitometry.
When microplates are used to hold samples for analysis using assay techniques which are dependant on the transmission of light through or from said samples, it is important to avoid transmission of light between adjacent samples, so-called "light crosstalk" and loss of light by transmission of light from the peripheral wells of the array, resulting in so-called "edge-effect" signal losses. "Light crosstalk" is extremely undesirable because it means that photons detected in any particular sample well may not have originated from the sample in that particular well. "Edge-effect" is similarly undesirable due to loss of photons from the peripheral sample wells resulting in inconsistent results from these wells. This edge-effect can be compensated for, to a certain extent, by adjustments to the software package of the analytical instruments.
It is the purpose of all assaying techniques to obtain a unique measurement for each sample that is fully representative of that sample. It is therefore necessary, when using multi-well components, to ensure the above mentioned cross-talk and edge-effect are reduced or eliminated altogether.
In certain applications it is necessary to have a transparent wall at the bottom of the sample well. These types of microplates can be used in a variety of instruments utilising photodetectors positioned either directly above the normally open end of the sample well, directly underneath the sample well or with photodetectors in both positions for coincidence measurement. It is obviously necessary in the latter two cases for the bottom of the well to be transparent to allow free passage of photons emitted by the sample.
It is also important in certain assays, which rely on the incubation of biological cell material within the sample wells, that the material from which the wells are manufactured is conducive to cell growth. Again, under certain circumstances, it is desirable for the bottom of the well to be transparent to allow microscopic viewing of adherent cells within the sample well.
Currently available microplates for either type of assay consist typically of a unitary polymer upper plate and a unitary polymer lower plate. The two plates are joined together by ultrasonic welding or similar methods. In this construction, the upper plate defines the side walls of the individual sample wells, and the lower plate defines the bottom walls of these wells. The upper plate is impervious to light, being either pigmented, or transparent but provided with an opaque coating at least on the side walls. The lower plate is transparent for the first type of assay in which transmission of light is monitored by through-viewing, and is generally opaque for the second type in which emission is monitored from above. In this second case the lower plate is made opaque through pigmentation or an opaque coating.
Microplates made as a single moulding with opaque side walls and opaque bottom walls are also known.
EP 571661 in the name of Packard is an example of a microplate which contains "opaque bands" projecting down into the lower plate which are intended to stop light passing from one well to another.
U.S. Pat. No. 5,039,860 in the name of Wallac features sample wells for emission type assays which have transparent bottom walls, for use in conjunction with an upper and a lower photomultiplier assembly. These sample wells are typically made by vacuum thermoforming (deep drawing) from a transparent polymer sheet.
U.S. Pat. No. 5,048,957 utilizes an aluminium matrix having through holes with annular shoulders therein, a transparent cuvette being located in each hole and resting on the said shoulder which defines its position in the through hole. The cuvettes are not bonded to the matrix.
WO 94/26413 provides a vessel or array of vessels in which each vessel has an axis, an open top, side walls and a base, the base incorporating a scintillant substance and the base being adapted for the attachment and/or growth of cells. The side walls are referred to as the main body of the vessel and may be pigmented. The base is attached to the side walls by bonding such as heat welding, injection moulding or ultrasonic welding. If there is any defect in such bonding leakage may occur from the vessel. The pigmenting of the side walls is said to eliminate optical crosstalk. However the transparent base plates are not masked from each other and radiation could leak from one base plate to another.
GB 1584589 discloses a multiwell plate which has a tray or matrix having a multiplicity of compartments in which individual wells are removably located in an upright position. The tray may be made of silicone rubber or foam polymer and the wells of glass or polymer material.
The wells are not bonded to the tray.
It is an objective of the present invention to provide an improved microplate, which includes well inserts with an integral clear base which permits sample viewing and/or measurement of light emissions from the sample, the wells being incorporated into an opaque matrix in such a way that it reduces cross-talk between adjacent wells.
It is an another objective of this invention to provide an improved method for manufacturing the sample wells, individually or as part of the microplate, which is both rapid and efficient.
Other advantages of the invention will become apparent upon reading the detailed description and upon reference to the accompanying drawings.